1. FIELD OF THE INVENTION
This invention relates to an EGR control device for an engine which performs a control wherein a portion of exhaust gas of an internal combustion engine is recirculated to an intake pipe of the internal combustion engine.
2. DISCUSSION OF BACKGROUND
Conventionally, an exhaust gas recirculation control device (hereinafter, EGR control device) performing a control of exhaust gas recirculation (hereinafter, EGR) as a means of decreasing NO.sub.x in the exhaust gas of the internal combustion engine, has widely been used. This EGR control device performs the control of EGR by an exhaust pressure control system utilizing a BPT (Back Pressure Transducer) valve.
Since the above-mentioned conventional EGR control device is constructed by using a BPT valve or the like, it can not detect an exhaust gas recirculation quantity, that is, an EGR flow quantity. As a result, when the EGR flow quantity is increased by deterioration of the BPT valve or the like, the drivability is worsened. Furthermore, when the EGR flow quantity is decreased, the NO.sub.x component in the exhaust gas is increased since the temperature of the engine is elevated.
Furthermore, even when this device is in an abnormal state by deteriorations of parts of the EGR control device, this abnormality is hard to be detected.